The invention relates to improvements in seating facilities in general, and more particularly to improvements in adjustable seats wherein a back rest is pivotable relative to a body supporting portion or base in response to rotation of a driving member which can change the inclination of first leaves of two hinge joints relative to second leaves, the first leaves being secured to the back rest and the second leaves being secured to the base of the seat.
Seats with pivotable or tiltable back rests are disclosed in numerous pending United States patent applications and in numerous United States and foreign patents of the assignee of the present application. Reference may be had, for example, to U.S. Pat. No. 4,708,392 granted Nov. 24, 1987 to Werner et al. for "Hinge joint for the seats of automotive vehicles and the like", and to U.S. Pat. No. 4,715,656 granted Dec. 29, 1987 to Walk et al. for "Hinge joint for the seats of motor vehicles and the like". As a rule, each hinge joint comprises a gear transmission which operates between the respective first and second leaves.
Commonly owned German Offenlegungsschrift No. 27 24 047 of Barthodziej et al. discloses a seat wherein the pintles of the two hinge joints are connected to each other by a torque transmitting shaft so that it suffices to provide a rotary driving member (such as a hand wheel) for one of the pintles whereby the shaft transmits torque from the one pintle to the other pintle. In order to compensate for play between the teeth of mating gears in each of the hinge joints, the shaft which is used in the seat of Barthodziej et al. is assembled of two coaxial sections which are coupled to each other by a sleeve or muff in such a way that the composite shaft can reduce the aforementioned play in each of the gear transmissions and the shaft also reduces the likelihood of staggering or stepwise transmission of motion from the one pintle to the other pintle in response to rotation of the driving member. This is achieved in that the two sections of the shaft are turned relative to each other prior to insertion of their neighboring ends into the sleeve so that such turning of the shaft sections eliminates the play between the teeth of gears in the respective transmissions. Thus, the teeth of one gear in one of the hinge joints bear against the left-hand flanks of the mating teeth, and the teeth of one gear in the other hinge joint bear against the right-hand flanks of the mating teeth. The neighboring end portions of the shaft sections are splined and the sleeve has internal grooves for the splines of the two sections so that the angular positions of the properly assembled shaft sections cannot be changed when the seat embodying such hinge joints is in use. It has been found that the composite shaft can reliably eliminate play between the mating teeth of the two gear transmissions and can also eliminate clearances between rotary parts and their bearings as well as unpredictable (stuttering) transmission of rotary motion from that pintle which is directly connected with the rotary driving member to the other pintle.
A drawback of the proposal of Barthodziej et al. is that the mounting of the shaft sections in the internally grooved sleeve necessitates the application of a greater force in order to change the inclination of the back rest. The problem is compounded by tolerances in the gear transmissions (particularly if the gears are out of round).